Description:
The Thelodontia are a group of fishes most commonly known from their
distinctive tooth-like scales. Indeed the term Thelodont , derived
from Greek, means nipple tooth. The teeth have a characteristic
crown made of dentine. The scales even on a single specimen are
quite variable, as can be seen here. Thelodonts are rarely found
as complete specimens; those that are show them to be flattened
fish, many of which were bottom dwellers. Recent finds of intact
specimens from Canada show that they radiated into some deep-bodied
forms that swam freely in the water column. These deep-bodied forms
may have been more closely allied with jawed fishes than their other
relatives. All Thelodonts were extinct by the Upper Devonian.

This
is a huge example of the taxon; a more “normal” size
example is shown alongside. The sketch shown what Longanellia looked
like in life.